(1) Field of the Invention
This invention relates to a capstan bearing device for a cassette tape recorder.
(2) Description of the Prior Art:
Capstan bearing devices for cassette tape recorders had such a structure as shown in FIG. 5. Namely, FIG. 5 is a vertical cross-section of a typical conventional capstan bearing device. A cylindrical bearing main body 2 is fixed on a base plate 1 by means of screws or the like. The bearing main body 2 in turn supports the lower half portion of a capstan 4 by way of bearing metals 3. The capstan 4 is also supported at the lower end thereof by a support 5 mounted on the rear side of the base plate 1, whereby the capstan 4 is prevented from slipping off the bearing main body 2.
A flywheel 6 is provided on the capstan 4 at a position below the bearing main body 2. Moreover, such a capstan bearing device is required to pass successfully through a severe impact or shock test which is performed in the final stage of the manufacturing process. In the structure depicted in FIG. 5, it was hence essential to use a durable member as the support 5 which supports the lower extremity of the capstan 4. This requirement hence led to a problem of high manufacturing cost. In addition, the above structure required an irksome operation for mounting the support 5.
With a view toward overcoming the above-described problem, it has been proposed to employ such a structure as shown in FIG. 6 instead of supporting the capstan 4 at the lower extremity thereof. In FIG. 6, an annular groove 7 is formed in the capstan 4 at an axially central part thereof. The annular groove 7 is positioned right above the upper end of the bearing main body 2 and a stopper washer 8 is fit in the annular groove 7 so as to prevent the capstan 4 from slipping off the bearing main body 2 downwardly.
In the above structure, the capstan 4 receives pressing forces from an associated pinch roller 9 at a position above the annular groove 7. As a result, stress is concentrated on the annular groove defining part of the capstan 4, where the capstan 4 is rendered thinner locally. The above structure is hence accompanied by a problem that the strength of the capstan 4 is reduced to a significant extent.
With the foregoing in view, it has been contemplated to employ such as structure as illustrated in FIG. 7. Namely, a bearing main body 11 has a greater length. An opening 12 is formed through a part of the peripheral wall thereof so as to receive the associated pinch roller 9 therethrough. The capstan 4 is rotatably supported at both ends of the bearing main body 11 by way of bearing metals 3 respectively. Further, an annular groove 13 is formed in an upper end portion of the capstan 4, in which a washer 8 is fit so as to prevent the capstan 4 from slipping off the bearing main body 11 downwardly. In application, the bearing main body 11 is inserted in a capstan insertion hole 15 of a tape cassette 14.
However, the provision of the opening 12 through the peripheral wall of the bearing main body 11 causes the bearing main body 11 to undergo bending deformation and as a result, the axes of the bearing metals 3 provided at both ends of the main bearing body 11 are rendered out of registration. The axes of the bearing metals 3 can be brought into coincidence if both inner end peripheral walls of the bearing main body 11 are machined for their centering after fabrication of the bearing main body 11 through a die or the like. Due to the formation of the opening 12 through the part of the peripheral wall, the bearing main body 11 undergoes gradual bending deformation in the course of its use over a long period of time so that the axes of both bearing metals 3 are rendered out of registration, leading to a problem that the smooth rotation of the capstan 4 is impaired.